Coating for ferrous metals



Patented Aug. 16, 1932 1,872,614

UNITED STATES PATENT OFFICE RALPH J. WIRSHING AND HENRY R. FAAS, OFDETROIT, MICHIGAN, ASSIGNORS TO GENERAL MOTORS RESEARCH CORPORATION, OFDETROIT, MICHIGAN, A. CORPO- RATION OF DELAWARE comma non rnnnous METALSNo Drawing. Application filed August 1, 1929. Serial No. 382,827.

The invention relates to the coating of Many of these sub-coatings whichwould be metal surfaces, especially of iron or steel or desirable fromthe standpoint of their proalloys thereof herein referred to as ferroustective effect are unsuitable for the reason metals. The type of coatingwith which the that the lacquer or enamel does not adhere invention isparticularly concerned is that in satisfactorily to the surface of thecoating 50 which one layer of a composite coating con material. e havefound,however, that tin sists of a metal preferably electrolytically andchromium possess to a high degree the deposited, and another layerconsists of a properties desirable for this use. Both of lacquer orenamel. these metals are extremely efficient in pre- In the finishing ofmetal parts, for exventing corrosion of ferrous metals by at- 55 ample,the sheet metal body or chassis parts mospheric or other commoncorrosive of automobiles, it is customary to apply to agencies and thelacquer with its priming ferrous metal surfaces a lacquer or enamelcoatings as well as baked japan or enamel coating. Lacquers usuallyemployed for coatings adhere to them very satisfactorily,

- this purpose are of the pyroxylin type, these the combinationafiording a highly efficient 60 being applied over one or morepreliminary and permanent finish for withstanding severe or primingcoats in the nature of oil paints. service conditions. It is preferredto apply These priming coatingsare usually dried at, the metal a ing byl r pla ing and any elevated temperatures. The enamels comusual methodof depositing these metals is 10 monly used, especially for the coatingof applicable. Chromium suffers the disad- 65 arts such as hoods andfenders, areof the vantages that its plating baths do not possess bakedenamel or baked japan type, conas high throwing power as tin platingbaths, taining asphalt and linseed oil. A typical hence tin is somewhatmore suitable for apcomposition of this type may contain application tosurfaces of irregular contour.

proximately 100 lbs. asphalt, 20 gallons lin- Tin or high tin alloymight, of course, be ap- 7 seed oil and 4 lb. lead oxide, whichingreplied by dipping the article in a fused bath dients are mixed withabout an equal volume of the metal, but we prefer electrolytic depoofsome thinner such as petroleum naphtha. sition by reason of the facilitywith which These baking enamels are usually applied in the coating maybe applied, the superior adseveral coats each of which is baked on at ahesion of the lacquer or enamel to the elec- 75 temperature in theneighborhood of 450 F. trodeposited coating, and the uniform disfor ahalf hour or more. Finishes of these tribution and the ease of controlof thickty es, however have not been found capable ness of the deposit.The electrolytic deof satisfactorily withstanding atmospheric posit hasa slightly roughened surface or and other corrosive agenciesundersomeofthe -O Which Con ributes to the adhesion Sn severe conditionsto which articles such as of the subsequently applied liquid coatingautomobiles are subjected. Exposure to salt composition. water or seaair, for example, cause rusting The temperature at which the baking ofthe metal under the lacquer or enamel namel re baked is usually abovethe meltwith the result that the coating is lifted from ing point oftin, but we have found that a 85 the surface and falls away in a es.thin electrolytic deposit of tin will remain In an effort to overcomethis difficulty we in position under the enamel during the bakhaveexperimented with numerous combinaing process. Chromium, of course, iscapations of sub-coatings designed to afford inble of withstandingwithout change any creased protection to the metal surfaces. temperaturerequired for baking.

tures.

RALPH J. WIRSHING. HENRY R. FAAS.

